Various methods are known for reducing toxic components, such as hydrocarbons, carbon monoxide and nitrogen oxides, contained in the exhaust gases discharged from an internal combustion engine. One such method comprises injecting the fuel into an auxiliary combustion chamber, wherein it is ignited by a spark ignition plug and burns, whereupon the combustion flames in the auxiliary combustion chamber spread into a main combustion chamber which is supplied solely with air for re-combustion. In this method, known as the stratified combustion method, the air in the main combustion chamber is forced into the auxiliary combustion chamber during the compression stroke of the engine, whereupon a charge of fuel is injected into the auxiliary chamber to form a rich fuel-air mixture, which mixture is ignited in the auxiliary chamber by the spark ignition plug and burns. Thus, the production of nitrogen oxides can be minimized by burning a rich fuel-air mixture in the auxiliary combustion chamber, and a reduction in the hydrocarbon and carbon monoxide content can then be accomplished by means of the re-combustion in the main combustion chamber. Further, this re-combustion in the main combustion chamber is carried out in the presence of excess oxygen at relatively low temperatures, so that nitrogen oxides will not be produced in this process.
However, this stratified charge method has a disadvantage in that the air forced from the main combustion chamber into the auxiliary combustion chamber during the compression stroke often causes a strong swirling of the gases inside the auxiliary combustion chamber. Thus, if the spark ignition plug is not installed in a proper position, the spark may be blown out. In addition, this method produces a large quantity of hydrocarbons during combustion because the fuel-air mixture in the auxiliary combustion chamber is not uniformly distributed.
In addition, it has been discovered that the location of the spark plug within the auxiliary combustion chamber significantly effects the combustion within the auxiliary chamber, and prevents a proper stratified combustion within the main chamber. For example, U.S. Pat. No. 2,735,413 discloses an engine utilizing an auxiliary chamber formed as an annulus and having a spark plug positioned deeply in the chamber so that it is spaced a substantial distance from the connecting passage which joins the auxiliary chamber to the main chamber. When the spark plug is positioned in this manner, substantial quantities of unburnt or incompletely burnt fuel-air mixture are blown out of the auxiliary combustion chamber into the main combustion chamber due to the substantial pressure increase resulting from the burning within the auxiliary chamber, which pressure increase is initiated adjacent the spark plug and then spreads toward the connecting passageway. This thus forces the unburned fuel-air mixture into the main combustion chamber, and results in an insufficient stratified combustion within the main combustion chamber, and also results in the production of undesired amounts of hydrocarbons and carbon monoxide. This relationship also produces undesired engine noise.
Thus, the object of this invention is to provide a combustion chamber structure for a spark-ignition type internal combustion engine, in which the above-described disadvantages are effectively overcome by positioning the spark plug in the auxiliary combustion chamber directly adjacent the end of the transfer passage which joins the auxiliary and main combustion chambers, whereby substantially all of the rich fuel-air mixture is burnt within the auxiliary combustion chamber and is not forced into the main combustion chamber, and wherein some of the burnt gases in the auxiliary combustion chamber are immediately blown out into the main combustion chamber to initiate combustion therein and thereby result in a less rapid pressure rise within the auxiliary combustion chamber coupled with a reduction in engine noise.
The present invention is characterized by positioning an obstacle, such as a substantially spherical or cylindrical obstacle, in the auxiliary combustion chamber of a combustion chamber structure which includes a main combustion chamber supplied solely with air through an intake valve, which auxiliary combustion chamber has a fuel injection nozzle and a spark ignition plug associated therewith, and a passage interconnecting the main and auxiliary combustion chambers. In the auxiliary combustion chamber according to this invention, the fuel-air mixture rotates around the obstacle, whereby the fuel is uniformly distributed in the mixture and thereby the ignitability of the mixture is increased. Further, by positioning the obstacle close to some portion of the interior wall of the auxiliary combustion chamber, the flow velocity around the obstacle can be varied so that blowing out of the spark arc can be prevented by installing the spark ignition plug at a location where the fuel-air mixture flows at low speed. As noted above, the spark plug is positioned directly adjacent the end of the transfer passage which connects the auxiliary and main combustion chambers.